For anyone looking at gaming controllers, I cannot recommend ControllerMate enough. USBOverdrive is classic and simple, but the level of controls CM offers is truly wonderful.
I have been looking at Leap Motion for the possibility of motion-based kerning control, but the SDK was a mess (both Python and Obj-C) and I stopped putting effort.
Also for anyone wanting to get rid of arm pain, keeping your wrist vertical can be very helpful. I recommend that you investigate vertical or pen-shaped mice as well.
https://www.posturite.co.uk/ergonomic-mice/vertical-mice.html